Method and device for detecting a target by masked high energy reflectors

ABSTRACT

Methods and devices for detecting, in a scene, a first type reflector is provided. The method includes identifying, using a radar in a mobile system, a zone of a distance-radial velocity space that contains a second type reflector. The second type reflector is capable of concealing the first type reflector. The method includes modeling an order two phase shift over time of theoretical first type and second type reflectors. The method includes creating a filter a distance and a radial velocity. The method includes illuminating the scene. The method includes acquiring raw radar data from the echoes reflected by the reflectors of the scene. The method includes obtaining distance profiles. The method includes applying a filter on the distance profiles. The method includes detecting the first type reflector among the second type reflector.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims the benefit of French Patent Application No. 1156126, filed Jul. 6, 2011, and titled “PROCEDE ET DISPOSITIF DEDETECTION D'UNE CIBLE MASQUEE PAR DES REFLECTEURS DE FORTE ENERGIE,”which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of the processingof the signal from a mobile, airborne radar. The disclosure relates todetection of a low-energy target that may be concealed by high-energyreflectors.

Conventional radars use radial velocity distance cartography to separatethe echoes from all of the targets in terms of distance and velocity.This amounts to positioning the targets in a radial velocity distancespace discretized in cells, in a manner known by those skilled in theart, as shown in FIG. 15 b.

In that figure, one pylon PYL1 is situated at a distance d1 from theradar system; two pylons PYL2 and PYL3 are situated at a same distanced2, but seen from different angles, as shown in FIG. 8.

Using conventional distance processing, the radar system obtains avector, called the distance profile, illustrated in FIG. 15 a. In thisprofile, the pylon PYL1 will generate a local energy maximum in thedistance cell corresponding to the distance d1. Likewise, the pylonsPYL2 and PYL3, which are located at the same distance d2 from thesystem, will generate a local energy maximum in the cell correspondingto said distance d2.

This distance processing makes it possible to distinguish the pylon PYL1from the pylons PYL2 and PYL3 on the distance profile. It does not,however, make it possible to distinguish between pylons PYL2 and PYL3.

To resolve this problem, velocity processing is conventionally applied.The output of this processing over all of the observed distancesconstitutes a distance-radial velocity cartography of the environment ofthe system, and is diagrammatically illustrated in FIG. 15 b.

Owing to this velocity processing, it is now possible to distinguishbetween the two pylons PYL2 and PYL3. In fact, since they are seen fromdifferent angles, they have different radial velocities relative to theradar system, as illustrated by FIG. 9. Once this velocity difference isgreater than the velocity resolution of the system, the two pylons PYL2and PYL3 appear in different velocity cells.

Using conventional means, targets may be separated from their directenvironment by comparing the relative energy levels on the distancevelocity cartography, this direct environment being able to be made uponly of noise, periodic reflectors, or extended reflectors. For example,and as shown in FIG. 16, a target 60 having energy greater than theclutter 50 can be separated from the latter.

However, a mobile target C situated in the direct environment of thepylon PYL2 (see FIG. 10), and the energy of which is at the same levelas that of PYL2, is concealed by the pylon and cannot be detected.

In certain flight and observation configurations, the strong echoes cantherefore lastingly conceal targets and prevent them from beingdetected. This concealment may also be caused by folding phenomena.

One solution may be to try to eliminate the aliasing phenomena byvarying the repetitive frequency of the radar waves. This method can beused when the target is found by velocity folding in the zone of theclutter, and consists of moving the aliasing velocity so that the targetis located outside the zone of the clutter for one of the repetitivefrequencies. However, there is may be no repetitive frequency that makesit possible to observe the target outside the clutter zone. Thissolution may not be fully satisfactory.

Another solution may be to use algorithms of the STAP (Space TimeAdaptive Processing) type and antenna arrays to reduce strong targetssuch as ground clutter. The STAP algorithms use an array of horizontalreceiving antennas to exploit the angle of arrival of the targets and todiscriminate along the azimuth angle in the Doppler plane, the radialvelocity of an echo of the clutter being connected to its angle ofarrival. However, using arrays of antennas and applying STAP algorithmsimposes major constraints on the sizing of the system and increases theprocessing complexity.

Another solution may be to separate targets using the polarimetricproperties of the targets and the clutter. This method requires at leasttwo transmitting antennas and at least two receiving antennas, whichmakes its implementation more complex.

Also a method was presented by Wang et al. in the document “Maneuveringtarget detection in over-the-horizon radar using adaptive clutterrejection and adaptive chirplet transform,” and published on Nov. 4,2003, in the review IEE Proc. Radar Navig, Vol 150, No 4. This methodmakes it possible to detect moving targets on sea clutter by rejectingclutter through projection, then performing an iterative two-dimensionalvelocity processing through chirplet transform on the signal. However,this method is only applicable to a fixed radar. It may not be effectiveto reject ground clutter.

SUMMARY OF THE INVENTION

One embodiment of the invention relates to a method for detecting, in ascene, at least one reflector of a first type. The method includesidentifying, using a radar in a mobile system, a zone of adistance-radial velocity space that may contain at least one reflectorof a second type. The at least one reflector of the second type iscapable of concealing the at least one reflector of the first type. Themethod includes modeling an order two phase shift over time oftheoretical reflectors of the first type and theoretical reflectors ofthe second type. The modeling uses a kinematic signature of thetheoretical reflectors. The order two phase shift is due to the Dopplereffect. The method includes creating a filter for at least one distanceand at least one radial velocity. The filter is computed from (a) aphase shift of the at least one reflector of the first type, at the atleast one distance and the at least one radial velocity; and (b) a phaseshift of the at least one reflector of the second type, at the at leastone distance and for each of the radial velocities of the zone. Thephase shifts are computed from the modeling of the order two phaseshift. The filter is configured to attenuate, by projection, the energyof the at least one reflector of the second type and to increase, bycorrelation, the energy of the at least one reflector of the first type,at the at least one distance and the at least one radial velocity. Themethod includes illuminating the scene. The method includes acquiringraw radar data from the echoes reflected by the reflectors of the scene.The method includes obtaining distance profiles. The distance profilesare obtained by processing raw radar data to separate the reflectors ofthe scene in terms of distance. The profiles are collected over a longtime. After the long time, the distance variation of a reflector of thescene to be considered quadratic relative to the time. The methodincludes applying a filter on the distance profiles. Applying the filtercomprises separating the reflectors of the scene in velocity. The methodincludes detecting the at least one reflector of the first type amongthe at least one reflector of the second type.

Another embodiment of the invention relates to a tangiblecomputer-readable storage medium, with computer-executable instructionsembodied thereon that when executed by a computer system perform amethod for detecting, in a scene, at least one reflector of a firsttype. The instructions include identifying, using a radar in a mobilesystem, a zone of a distance-radial velocity space that may contain atleast one reflector of a second type. The at least one reflector of thesecond type is capable of concealing the at least one reflector of thefirst type. The instructions include modeling an order two phase shiftover time of theoretical reflectors of the first type and theoreticalreflectors of the second type. The modeling uses a kinematic signatureof the theoretical reflectors. The order two phase shift is due to theDoppler effect. The instructions include creating a filter for at leastone distance and at least one radial velocity. The filter is computedfrom (a) a phase shift of the at least one reflector of the first type,at the at least one distance and the at least one radial velocity; and(b) a phase shift of the at least one reflector of the second type, atthe at least one distance and for each of the radial velocities of thezone. The phase shifts are computed from the modeling of the order twophase shift. The filter is configured to attenuate, by projection, theenergy of the at least one reflector of the second type and to increase,by correlation, the energy of the at least one reflector of the firsttype, at the at least one distance and the at least one radial velocity.The instructions include illuminating the scene. The instructionsinclude acquiring raw radar data from the echoes reflected by thereflectors of the scene. The instructions include obtaining distanceprofiles. The distance profiles are obtained by processing raw radardata to separate the reflectors of the scene in terms of distance. Theprofiles are collected over a long time. After the long time, thedistance variation of a reflector of the scene to be consideredquadratic relative to the time. The instructions include applying afilter on the distance profiles. Applying the filter comprisesseparating the reflectors of the scene in velocity. The instructionsinclude detecting the at least one reflector of the first type among theat least one reflector of the second type.

Another embodiment of the invention relates to an apparatus fordetecting, in a scene, at least one reflector of a first type. Theapparatus includes a radar configured to illuminate the scene and toacquire raw radar data from the echoes reflected by the reflectors ofthe scene. The apparatus includes means for identifying, using a radarin a mobile system, a zone of a distance-radial velocity space that maycontain at least one reflector of a second type. The at least onereflector of the second type is capable of concealing the at least onereflector of the first type. The apparatus includes means for modelingan order two phase shift over time of theoretical reflectors of thefirst type and theoretical reflectors of the second type. The modelinguses a kinematic signature of the theoretical reflectors. The order twophase shift is due to the Doppler effect. The apparatus includes meansfor creating a filter for at least one distance and at least one radialvelocity. The filter is computed from (a) a phase shift of the at leastone reflector of the first type, at the at least one distance and the atleast one radial velocity; and (b) a phase shift of the at least onereflector of the second type, at the at least one distance and for eachof the radial velocities of the zone. The phase shifts are computed fromthe modeling of the order two phase shift. The filter is configured toattenuate, by projection, the energy of the at least one reflector ofthe second type and to increase, by correlation, the energy of the atleast one reflector of the first type, at the at least one distance andthe at least one radial velocity. The apparatus includes means forobtaining distance profiles. The distance profiles are obtained byprocessing raw radar data to separate the reflectors of the scene interms of distance. The profiles are collected over a long time. Afterthe long time, the distance variation of a reflector of the scene to beconsidered quadratic relative to the time. The apparatus includes meansfor means for applying a filter on the distance profiles. Applying thefilter comprises separating the reflectors of the scene in velocity. Theapparatus includes means for means for detecting the at least onereflector of the first type among the at least one reflector of thesecond type.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present disclosure will emerge fromthe description below, in reference to the appended drawings, whichillustrate one embodiment thereof that is in no way limiting. In thefigures:

FIG. 1 shows a flowchart illustrating the main steps of a detectionmethod, according to an exemplary embodiment

FIG. 2 shows a flowchart illustrating a step for acquiring raw radardata that may be used in the invention, according to an exemplaryembodiment;

FIG. 3 shows a flowchart illustrating a step for obtaining distanceprofiles that may be used in the invention, according to an exemplaryembodiment;

FIG. 4 shows a flowchart illustrating one example of a step foridentifying a ground clutter zone, according to an exemplary embodiment;

FIG. 5 shows a flowchart illustrating a modeling step that may be usedin the invention, according to an exemplary embodiment;

FIG. 6 shows a flowchart illustrating a filter application and targetdetection step that may be used in the invention, according to anexemplary embodiment;

FIG. 7 shows a flowchart illustrating a step for creating filters thatmay be used in the invention, according to an exemplary embodiment;

FIGS. 8-10 shows pylons relative to a radar system, according to anexemplary embodiment;

FIG. 11 shows the mobile system and the geometric parameters making itpossible to calculate a priori the radial velocities of reflectors onthe ground situated at a distance d from the system, according to anexemplary embodiment;

FIG. 12 shows a mobile system comprising a device, according to anexemplary embodiment;

FIGS. 13-14 shows the result of velocity processing obtained usingconventional means and by applying the filters of FIG. 6, respectively,according to exemplary embodiments;

FIGS. 15 a-15 b, show the reflectors of the scene of FIG. 8 over adistance profile and over a distance-velocity cartography, respectively,according to exemplary embodiments;

FIG. 16 shows, in a distance-radial velocity cartography, the reflectorsof a scene comprising a target in a high-energy zone, according to anexemplary embodiment;

FIG. 17 shows, in the distance-radial velocity space, reflectors andhigh-energy zones, according to an exemplary embodiment;

FIG. 18 shows, in certain hypotheses, the position of the high-energyzone corresponding to the ground clutter in the distance-radial velocityspace, according to an exemplary embodiment; and

FIG. 19 shows a scene including a radar, reflectors, and the reflectors'echoes, according to an exemplary embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to an exemplary embodiment, a method implemented in a mobilesystem comprising a radar for detecting, in a scene, at least one targetreflector of a first predetermined type, called target type, that may beconcealed by at least one high-energy reflector of a second type, calledstrong type, is disclosed. This method may comprise:

a step for identifying a zone of the distance-radial velocity space thatmay contain high-energy reflectors capable of concealing the targetreflectors;

a step for modeling the order two phase shift over time, due to theDoppler effect, of target reflectors and strong reflectors, the modelingusing the kinematic signature of said theoretical reflectors;

a step for creating a filter for at least one distance and one radialvelocity given by: the phase shift of a theoretical target reflector atthat distance and for that radial velocity; and the phase shift of atheoretical strong reflector at that distance and for each of the radialvelocities of the zone, said phase shifts being obtained from theaforementioned modeling, said filter being designed to attenuate, byprojection, the energy of the high-energy reflectors of said scene andincrease, by correlation, the energy of the target reflector(s) of thescene at the given distance and for the given radial velocity;

a step for illuminating the scene and acquiring raw radar data from theechoes reflected by the reflectors of the scene;

a step for obtaining distance profiles obtained by processing raw radardata to separate the reflectors of the scene in terms of distance, saidprofiles being collected over a long enough time for the distancevariation of a reflector of the scene to be able to be consideredquadratic relative to the time;

a step for applying filters on said distance profiles, this step leadingto a separation of the reflectors of the scene in velocity; and

a step for detecting the target reflectors among the high-energyreflectors.

Correlatively, the disclosure relates to a device that may beincorporated in a mobile system to detect, in a scene, at least onetarget reflector of a first predetermined type, called target type, thatmay be concealed by at least one high-energy reflector of a second type,called strong type. The mobile system may comprise:

a radar capable of illuminating the scene and acquiring raw radar datafrom the echoes reflected by the reflectors of the scene;

means for identifying a zone of the distance-radial velocity space thatmay contain high-energy reflectors capable of concealing the targetreflectors;

means for modeling the order two phase shift over time, due to theDoppler effect, of target reflectors and strong reflectors, the modelingusing the kinematic signature of said theoretical reflectors;

means for creating a filter for at least one distance and one radialvelocity given by: the phase shift of a theoretical target reflector atthat distance and for that radial velocity; and the phase shift of atheoretical strong reflector at that distance and for each of the radialvelocities of the zone; said phase shifts being obtained from theaforementioned modeling, said filter being designed to attenuate, byprojection, the energy of the high-energy reflectors of said scene andincrease, by correlation, the energy of the target reflector(s) of thescene at the given distance and for the given radial velocity;

means for obtaining distance profiles obtained by processing raw radardata to separate the reflectors of the scene in terms of distance, saidprofiles being collected over a long enough time for the distancevariation of a reflector of the scene to be able to be consideredquadratic relative to the time;

means for applying filters on said distance profiles, this step leadingto a separation of the reflectors of the scene in velocity; and

means for detecting the target reflectors among the high-energyreflectors.

The following exemplary definitions are used to introduce thedisclosure:

Long time: “long time” refers to a long enough observation time of thescene for the distance variation of a target to be able to be consideredquadratic (approximation of order two) relative to the time. For aradar, the observation time of the scene corresponds to the echocollection time.

The Doppler phase shift being directly proportional to the variation ofthe distance, it is also quadratic, or in other words “of order 2.” Thelinear term of this phase shift, called order 1, is a function of theradial velocity of the target, and the quadratic term called order 2 isa function of the radial acceleration and the orthoradial velocity ofthe target. This observation time, typically longer than 1 second inthis invention, is generally not used by detection radars, but rather byimaging radars.

Short time: “short time” refers to an observation time of the scene suchthat the distance variation of a target may be considered linear(approximation to order one) relative to the time.

The Doppler phase shift being directly proportional to the variation ofthe distance, it is also linear, or in other words, “order 1.”

The detection radars typically make this approximation and use standardobservation times in the vicinity of several tens of milliseconds in thestate of the art.

Radial velocity and orthoradial velocity: according to the state of theart, the radial velocity of a target refers to the projection, on theaxis connecting the target to the carrier, of the relative velocity ofthe target in relation to the carrier. The orthoradial velocity refersto the component, normal to the radial velocity, of the relativevelocity of the target in relation to the carrier.

The velocities verify the following equation (FIG. 10):Vrel² =Vrad² +Vorth²  (eq. 1)where Vrel is the relative velocity of the target in relation to thecarrier.

Kinematic signature: The kinematic signature is the relationship thatconnects the orthoradial velocity and the radial velocity of a target,said velocities being relative in relation to the mobile system. Thekinematic signature corresponds to a particular kinematic behavior of atarget in relation to the system.

Fixed ground reflector: “Fixed ground receptor” refers to the reflectorshaving a zero airspeed. From the platform, their relative velocity isequal to the movement velocity of the platform and in the oppositedirection. For example, in FIG. 9, the pylons PYL2 and PYL3 have arelative velocity “−Va” from the platform.

The kinematic signature of these reflectors verifies the equation:Va ² =Vrad² +Vorth²  (eq. 2)where Va is the velocity of the carrier, which may for example beprovided by an onboard GPS.

In particular, the ground clutter is made up of a multitude ofelementary reflectors fixed to the ground having the kinematic signaturegiven by equation (2).

Target collision reflector: “Target collision reflector” refers to thetarget reflectors whereof the path will cross that of the system. Theyhave a radial velocity oriented toward the system and a zero orthoradialvelocity:Vorth²=0  (eq. 3)

The detection method and device, according to an exemplary embodiment,may advantageously be used in a radar system comprising only onetransmitting antenna, only one receiving antenna, and only onerepetitive frequency. This makes it possible to obtain a clutterrejection system in particular having a low cost and complexity relativeto the clutter rejection systems for mobile radars known to date.

The solution according to the disclosure can in particular be used todetect collision targets concealed by the ground clutter.

As a result, in a first particular embodiment, the kinematic signatureof the target reflectors is defined by a zero orthoradial velocity.

Advantageously, the modeling used by the invention, in particular forthe clutter, does not require secondary data.

Furthermore, the velocity processing according to the invention is doneover a single velocity dimension (defined by the target signature), anddoes not require successive iterations. The velocity processing of theprior art proposed by Wang is an iterative processing with twodimensions that is much heavier in terms of computation time, compoundedby the need for an iteration to detect the targets with lower energylevels.

According to an exemplary embodiment, the filter used in the inventionis an oblique projection matrix known by those skilled in the art ofsignal processing.

This feature advantageously makes it possible to reject high-energyreflectors (for example, ground clutter) and to perform the velocityprocessing simultaneously, whereas the prior art separates theprocessing into two steps.

In various embodiments, the step for identifying a zone of the distancevelocity space comprises:

a step for building the distance-radial velocity cartography resultingfrom the raw radar data observed during a short time; and

a step for analyzing that cartography.

The construction of the distance-velocity cartography traditionallyconsists of applying the following processing: collection of raw radardata over a “short time,” separating targets in terms of distance usinga fast Fourier transform called distance FFT, and separating targets interms of radial velocity using so-called Doppler FFT processing.

The analysis of the cartography may be done in several ways.

A first solution uses conventional processing methods of processingimages and includes:

forming an image from the cartography, whereof the color choice is basedon the energy levels of the cartography, and whereof the contrast issufficient at least to differentiate the noise zones without reflectorsand the high-energy reflector zones,

applying image processing algorithms to segment the image into zones,for example by detecting contours, or by shape recognition when theshape of the zones of the high-energy reflectors is known,

classifying these zones, according to criteria, for example scope ortotal power, to identify the high-energy reflector zones that mayconceal the targets to be detected.

Another solution uses conventional processing and includes:

performing a detection by thresholding high-energy reflectors, forexample using a constant false alarm rate CFAR detection algorithm,

grouping the detections together in “clusters” or zones by clusteringalgorithm, for example closest neighbor algorithm,

classifying said clusters according to criteria, for example scope ortotal power of the cluster, to identify the high-energy reflector zonesthat may conceal the targets to be detected.

In various other embodiments, the step for identifying the zone in thedistance velocity space is performed from a priori knowledge of theobservation geometry, of the antenna diagram of said radar and, of thecharacteristics of the flight of the system.

According to an exemplary embodiment, the step for obtaining thedistance profiles comprises processing compensating for the distancemigration of the reflectors over the long time.

This processing makes it possible to offset the fact that the reflectorsmay change distance cells if their movement relative to the radar isgreater than the size of a distance cell.

According to an exemplary embodiment, the detection step uses a detectorof the CFAR type.

Alternatively, the step for detecting the target reflectors andestimating the noise level, for a distance-radial velocity cell, usesonly said collector distance profiles, at that distance.

According to an exemplary embodiment, the different steps of thedetection method according to the invention are determined byinstructions from computer programs embodied on tangiblecomputer-readable storage media.

Consequently, the disclosure also relates to a computer program embodiedon a tangible computer-readable storage medium, said program being ableto be run by a computer, said program comprising instructions adapted tothe implementation of the steps of a detection method as mentionedabove.

This program may use any programming language, and be in the form ofsource code, object code, or intermediate code between source code andobject code, such as in a partially compiled form, or in any otherdesired form.

The invention also relates to a tangible computer-readable storagemedium readable by a computer, and comprising instructions for acomputer program as mentioned above.

The tangible computer-readable storage medium may be any entity ordevice capable of storing the program. For example, the medium maycomprise a storage means, such as a ROM, for example a CD-ROM or amicroelectronic circuit ROM, or a magnetic recording means, for examplea disk (floppy disk) or a hard drive.

Furthermore, the information medium may be a transmissible medium suchas an electrical or optical signal, which can be conveyed by means of anelectrical or optical cable, radio, or by other means. The programaccording to the invention may in particular be downloaded on a networksuch as the Internet.

Alternatively, the tangible computer-readable storage medium may be anintegrated circuit in which the program is incorporated, the circuitbeing adapted to run or to be used in the execution of the method inquestion.

One application of the disclosure includes detection of a collisiontarget concealed by ground clutter.

In reference to FIGS. 1 to 19, various embodiments of a method and adevice making it possible to detect target reflectors are described.According to an exemplary embodiment, the target reflectors are of apredetermined type in a scene that may be concealed by high-energyreflectors.

In general, these methods and these devices apply, on data acquired byradar, to filters that may be created either from the data itself (firstalternative), or a priori, without using the radar, from generalknowledge of the scene and of characteristics of the radar and flightconditions (second alternative). The disclosure will primarily bedescribed in this second alternative embodiment.

According to an exemplary embodiment, the method according to thedisclosure implements six main steps illustrated in FIG. 1, i.e.:

a step P0 for acquiring raw radar data;

a step P1 for obtaining distance profiles for a long time;

a step P2 for identifying high-energy zones;

a step P3 for modeling the reflectors of the scene;

a step P5 for creating filters for a long time; and

a step P4 for applying said filters and detecting targets.

It appears in this figure that steps P2 for identification of zones, P3for modeling, and P5 for creating filters may be performed before,after, or in parallel with steps P0 for acquiring raw radar data and P1for obtaining distance profiles.

FIG. 12 diagrammatically shows a mobile system 100 comprising a radar110 and a device 10 according to the invention.

According to an exemplary embodiment, the radar 110 with range Dmaxcomprises an azimuth opening angle denoted φ. It uses a waveform of thefrequency-modulated continuous-wave (FMCW) type with central wavelengthlambda and frequency band B. It comprises a single transmitting antenna111 and a single receiving antenna 112, and performs a homodynedemodulation known by those skilled in the art.

According to an exemplary embodiment, the device 10 has the materialarchitecture of a computer. It in particular comprises a computationunit 11, a random-access memory of the RAM type 12, and a read-onlymemory of the ROM type 13.

This read-only memory 13 constitutes a medium within the meaning of theinvention. It comprises a computer program PG, which, when it is run bythe computation unit 11, executes instructions to implement the steps ofthe method of FIG. 1.

According to an exemplary embodiment, the device 10 comprises means 120for obtaining the velocity Va, altitude and attitude of the mobilesystem 100, for example by GPS and the inertial unit of the mobileplatform.

In reference to FIGS. 2, 12 and 19, an exemplary embodiment step P0 foracquiring raw radar data is described.

According to an exemplary embodiment, the radar 110 emits a wave 70 withshape FMCW that propagates in the scene (step E01). In this embodiment,the wave is emitted by the single transmitting antenna 111.

The emitted waveform is repeated by cycles of Tr seconds. This wave isbackscattered by each reflector of the scene in the form of echoes ofthe wave. Only two reflectors 50, 60 and their echoes 20, 30 are shownin FIG. 19. These echoes are then received by the single receivingantenna 112, which is distinct from the transmitting antenna 111 (stepE02).

The received signals are demodulated, sampled and quantified (step E03)to form raw radar data.

In reference to FIG. 3, an exemplary embodiment of a step P1 forobtaining distance profiles according to the disclosure is described.

The collection of the distance profiles may be done over a long time,within the meaning of the disclose.

More specifically, in this embodiment, this step P1 comprises thefollowing three sub-steps:

compensating for distance migration (step E11);

distance processing (step E12); and

distance profile collection (step E13).

More specifically, upon each repetition cycle Tr of the radar, thereflectors may be separated (step E12) by distance, for example by aFourier transform, to obtain a distance profile vector PDC containingdistance cells. The size of the distance cells corresponds to thedistance resolution of the radar c/2B, and contains energy and phaseinformation, which is the sum of the contributions of all of thereflectors situated at the considered distance.

During the long time used by the device 10, the reflectors can changedistance cells if their movement relative to the radar 110 is largerthan the size of a distance cell.

In this embodiment, the device 10 according to the invention establishes(step E11) RMC processing to compensate distance cell changes by thereflectors, changes due to the movement of the mobile platform, duringthe long time.

The conventional RMC processing is not be described in detail herein. Ituses the velocity Va of the mobile system 110, provided by the means 120previously described.

According to an exemplary embodiment, the device 10 collects distanceprofiles upon each cycle during a long time (step E13), and forms adistance-time matrix denoted MDT with M columns. In this MDT matrix:

a column is one of the distance profile vectors PDC calculated in stepE12; and

a row corresponds to the observation over time of the energy and thephase of a same distance cell d, and will be called time signal MDT(d)hereafter. The time signal MDT(d) represents the sum of the signals fromthe echoes of all of the reflectors situated in the distance cell d.

The choice of the number M of radar cycles defines the long time of theinvention; according to the invention, it is great enough for thedistance variation of the reflectors to be able to be consideredquadratic relative to the time:d(t)=d0+Vrad×t+½(Arad+Vorth² /d0)×t ²  (eq. 4)where d(t) represents the distance of a reflector at time t; d0represents the distance of said reflector at the initial time t=0; Vradrepresents the radial velocity of said reflector; Arad represents theradial acceleration of said reflector; and Vorth represents theorthoradial velocity of said reflector, Vrad, Arad and Vorth beingconsidered constant throughout the long observation time.

As a result, the phase shift due to the Doppler effect translating thedistance variation of the reflector relative to the mobile system 100 isquadratic in relation to the time.

This order 2 phase shift is written traditionally:2pi/lambda×(Vrad×t+½(Arad+Vorth² /d0)×t ²)  (eq. 5)in which lambda represents the central wavelength emitted by the radar110.

“Phase law of a reflector” refers to the complex exponential of itsphase shift during the time defined by equation (5):exp[j2pi/lambda×(Vrad×t+½(Arad+Vorth² /d0)×t ²)]

In general, step P2 identifies, in the distance-radial velocity space,one or more zones in which high-energy reflectors are situated that arecapable of concealing the target reflectors to be detected.

FIG. 17 presents an example of distance-radial velocity space in which:the points Ri, represented by x's, designate reflectors of the scene;and two zones Z1 and ZF designate high-energy zones, the J-shaped zoneZF representing the ground clutter zone.

According to an exemplary embodiment, the detection method and deviceaccording to the invention identify the high-energy zone ZFcorresponding to the ground clutter, the target reflectors to bedetected only being sought in that zone.

It will be recalled that the disclosure is described here in its secondalternative, and more specifically in an embodiment using the hypothesesof flat ground and horizontal stabilized flight, these hypotheses makingit possible to deduce, a priori and geometrically, the clutter zoneusing the velocity, the height of the mobile system 100 in relation tothe ground, and the angular observation zone of the scene.

According to an exemplary embodiment, and as shown in FIG. 4, step P2for identifying the clutter zone comprises the following threesub-steps:

determining the ground clutter distance range (step E21);

computing the radial velocities of the ground clutter at those distances(step E22); and

determining a zone covering the clutter zone (step E23).

In reference to FIG. 18, and in the preceding hypothesis of horizontalflight, the distance range in which the ground clutter is situated isdetermined (step E21), said range being bounded on the one hand by theheight h of the mobile system 100 relative to the ground, and on theother hand by the range Dmax of the radar 110.

For a given distance d, the device 10, according to an exemplaryembodiment, computes, during a step E22, the range [Vrad_min(d),Vrad_max(d)] of radial velocities corresponding to the ground clutter,using the following geometric relationships:

when |α|>φ/2:

$\begin{matrix}{{{{{Vrad\_ max}\mspace{11mu}(d)} = {V_{a}\sqrt{1 - \left( \frac{h}{d} \right)^{2}}{\cos\left( {\alpha - {\phi/2}} \right)}}}{{{Vrad\_ min}\mspace{11mu}(d)} = {V_{a}\sqrt{1 - \left( \frac{h}{d} \right)^{2}}{\cos\left( {\alpha + {\phi/2}} \right)}}}}\;} & \left( {{{eq}.\mspace{11mu} 6}\text{-}7} \right)\end{matrix}$when |α|<φ/2:

$\begin{matrix}{{{{Vrad\_ max}\mspace{11mu}(d)} = {V_{a}\sqrt{1 - \left( \frac{h}{d} \right)^{2}}}}{{{Vrad\_ min}\mspace{11mu}(d)} = {V_{a}\sqrt{1 - \left( \frac{h}{d} \right)^{2}}{\cos\left( {\alpha + {\phi/2}} \right)}}}} & \left( {{{eq}.\mspace{11mu} 6}\text{-}7} \right)\end{matrix}$in which: Va is the velocity of the mobile system 100; h is its heightrelative to the ground; d is the observation distance from the ground; φis the azimuth opening angle of the radar; α is the angle between thedirection of movement of the mobile system and the line of sight of theradar; as shown in FIG. 11.

As illustrated in FIG. 18, the ground clutter zone is in thecharacteristic shape of a J-hook in the distance-radial velocity space.

According to an exemplary embodiment, the detection method according tothe invention uses, for the continuation of the processing, a zone ZCcorresponding to the clutter zone ZF. In other embodiments, it ispossible to determine (during a step E23) a zone ZC covering the clutterzone ZF.

In general, during a step P3, the order two phase shift due to theDoppler effect of the reflectors of the scene is modeled.

To that end, the phase law given by equation (5) is used, verified forall of the reflectors, and their kinematic signatures to obtain amodeled phase shift depending only on the radial velocity and thedistance. This step P3, as shown in FIG. 1, is done on the one hand tomodel the phase shift of the strong reflectors and on the other hand tomodel the phase shift of the target reflectors.

More specifically, in this example, as shown in FIG. 5, the step P3comprises the following sub-steps:

Computation of the radial acceleration Arad (E32);

Computation of the orthoradial velocity Vorth(d) (E33); and

Creation of the model of the phase shift of the reflector (E34).

During step E32, the device 10 may compute the radial acceleration ofthe reflectors. In the embodiment described here, the device 10 uses thehypothesis of a horizontal stabilized flight and reflectors fixed on theground (strong reflectors within the meaning of the invention). Theradial acceleration Arad of the strong reflectors is therefore zero. Inthe embodiment described here, the interest is in the detection ofcollision targets (target reflectors within the meaning of theinvention). The radial acceleration Arad of the target reflectors istherefore also zero.

During step E33, the device 10 may compute the orthoradial velocity ofthe reflectors. This is obtained from the kinematic signature of thereceptor that connects the radial velocity Vrad and the orthoradialvelocity Vorth.

According to an exemplary embodiment, the kinematic signature of thestrong reflectors is predetermined. This signature is the kinematicsignature of the clutter given by equation (2). In other embodiments, itmay be obtained during flight, for example chosen by the pilot from akinematic signature database as a function of the scene.

According to an exemplary embodiment, the kinematic signature of thetarget reflectors is predetermined. In the example of collision targets,the kinematic signature of equation (3) is used.

During step E34, the device 10 may model the phase shift of thetheoretical reflectors. To that end, the order two phase shift expressedby equation (5), recalled below, is used.2pi/lambda×(Vrad×t+½(Arad+Vorth² /d0)×t ²)  (eq. 5)in which the values of Arad computed in step E32 are filled in and Vorthis replaced by its relationship to Vrad obtained in step E33.

According to an exemplary embodiment, two types of kinematic signaturesare used, which define two types of theoretical reflectors, i.e.“strong” theoretical reflectors and “target” theoretical reflectors,leading to two models.

In general, during a step P5, a filter may be is created for a givendistance and radial velocity. This filter is calculated:

from the phase shift of a target theoretical reflector at that distanceand for that radial velocity; and

from the phase shift of a strong reflector for that distance and foreach of the radial velocities of the zone ZC.

More specifically, in this embodiment, the step P5 comprises, inreference to FIG. 7:

a sub-step for creating a matrix of the phase shifts of the strongreflectors (step E52);

a sub-step for creating a matrix of the phase shifts of the targetreflectors (step E53);

a sub-step for computing an orthogonal projection matrix at a givendistance (step E54); and

a sub-step for creating a filter for a given distance and radialvelocity (step E55).

In step E52, the phase shift of a strong theoretical reflector may becomputed at the distance for which the filter is created for each of theradial velocities of the zone ZC, this phase shift being obtained fromthe model of step P3.

Likewise, in step E53, the phase shift of a target theoretical reflectormay be computed at the distance and for the radial velocity for whichthe filter is created, this phase shift being obtained from the modelstep P3.

For this given distance d, these phase shifts may be stored in a firstphase shift matrix MPF(d) (second phase shift matrix MPC(d),respectively), these phase shifts being computed at time k·Tr and atvelocities Vrad(d) (at the velocity Vrad for which the filter iscreated, respectively).

In this matrix, the indicator k varies in the rows and the radialvelocities Vrad vary in columns. The elements of this matrix are thephase shifts of theoretical reflectors and are written, in thisembodiment:

$\begin{matrix}{\exp\left( {j\; 2\;{\pi\left( {{\frac{2{{Vrad}(d)}}{\lambda}k\; T_{r}} + {\frac{{Vorth}^{2}(d)}{\lambda\; d}k^{2}T_{r}^{2}}} \right)}} \right)} & \left( {{eq}.\mspace{11mu} 6} \right)\end{matrix}$in which equation: k is an integer varying from 0 to M−1; the velocityVrad(d) is equal, for MPC(d), to the velocity for which the filter iscreated; and the velocity Vrad(d) varies, for MPF(d), from Vrad_min(d)to Vrad_max(d), following the velocity pitch Δv=λ/2MT_(r) where Δv isthe resolution in velocity of the radar 110; and Vorth(d) is obtainedfrom Vrad(d) using the kinematic signature of the theoretical reflectorsas described in step P3.

For the first matrix MPF(d), the kinematic signature of the strongreflectors may be used (equation (2)); for the second matrix MPC(d), thekinematic signature of the target reflectors may be used (equation (3)).In this way, a column of MPF(d) (MPC(d), respectively) models the phaseshift over time of a strong reflector (of a target reflector,respectively) at distance d and radial velocity Vrad. A row of MPF(d)(MPC(d), respectively) models the phase shift at a given moment of thestrong reflectors (of the target reflectors, respectively) at distanced.

The matrix MPF(d) (MPC(d), respectively) represents the noise sub-space(signal sub-space, respectively) of the strong reflectors (of the targetreflectors, respectively) and with constant amplitudes throughout thetime.

These two sub-spaces are distinct, since the kinematic signatures of thestrong and target reflectors are different.

The filter created during this step P5 may use a projection in relationto the noise sub-space.

In some embodiments, this projection is an orthogonal projection capableof attenuating the energy of the strong reflectors. It requires thecomputation of the orthogonal projection matrix in relation to the noisesub-space.

In other embodiments, this projection is an oblique projection capableof attenuating the energy of the strong reflectors and increasing theenergy of the target reflectors. It also requires the computation of theorthogonal projection matrix in relation to the noise sub-space.

During a step E54, the device 10 may compute this orthogonal projectionmatrix in relation to the noise sub-space.

The orthogonal projection matrix, denoted Porth(d), may be computed fromthe matrix MPF(d), which represents the noise sub-space. It is writtenin the following form:Porth(d)=I−MPF(d)·(MPF(d)*·MPF(d))⁻¹·MPF(d)*  (eq. 8)where I is the identity matrix and the operator * designates thetransconjugation operation of a matrix. By definition,Porth(d)·MPF(d)=0.

During a step E55, the device 10 may create a filter F(d, Vrad) for agiven distance and radial velocity from Porth(d). Various embodimentsare possible.

In some embodiments, the filter created during this step E55 is anorthogonal projection, followed by a correlation. This orthogonalprojection amounts to multiplying the time signal MDT(d) by theorthogonal projection matrix Porth(d):Porth(d)·MDT(d)Tin which equation the operator T designates the transposition operationof a matrix.

The correlation that follows the projection in these embodiments is donerelative to the signal sub-space defined by the matrix MPC(d), andamounts to multiplying the projection output signal by the column ofMPC(d) corresponding to the radial velocity Vrad and denotedMPC(d,Vrad):MPC(d,Vrad)*·Porth(d)·MDT(d)TThe filter F(d, Vrad) is then defined as follows:F(d,Vrad)=Porth(d)·MPC(d,Vrad)·MPC(d,Vrad)*·Porth(d)  (eq. 9)

In these embodiments, the filter therefore successively applies anorthogonal projection to attenuate the energy of the strong reflectors,and a correlation to increase the energy of the target reflectors.

Furthermore, this correlation amounts to performing velocity processingadapted to the kinematic signature of the target reflectors. In theseembodiments, the target reflectors are collision reflectors and have azero quadratic phase shift: the adapted velocity processing is forexample a discrete Fourier transform.

In other embodiments, the filter created during this step E55 is anoblique projection. The two signal and noise sub-spaces defined in theinvention may not be orthogonal. This may advantageously avoideliminating part of the signal sub-space. The use of an obliqueprojection may be better adapted to the two sub-spaces present

An oblique projection may use the orthogonal projection matrix at thenoise sub-space Porth(d), and the matrix MPC(d) representing the signalsub-space. The oblique projection matrix may be obtained from thefollowing equation:F(d,Vrad)=Porth(d)·p·(p*·Porth(d)·p)⁻¹ ·p*·Porth(d)  (eq. 10)in which p designates the column of MPC(d) at the velocity Vrad.

An oblique projection may make it possible simultaneously to attenuatethe energy of the strong reflectors and increase the energy of thetarget reflectors. It may also perform velocity processing adapted tothe kinematic signatures of the target reflectors.

According to an exemplary embodiment, the target reflectors to bedetected are sought in a processing zone ZT chosen in thedistance-radial velocity space. Generally, during a step P4, the filtersobtained in step P5 may be applied on the time signals obtained in stepP1, for the distances and radial velocities of the processing zone ZT,then a step is carried out to detect the target reflectors of the scene.

More specifically, step P4 comprises, in reference to FIG. 6:

a sub-step for applying filters (step E41);

a sub-step for estimating the noise (step E42); and

a sub-step for detecting the target reflectors (step E43).

During a step E41, the device 10 may apply the filters F(d,Vrad) on thetime signals MDT(d), for each distance d and radial velocity of the zoneZT, so as to obtain the distance velocity matrix MDV:MDV(d,Vrad)=|MDT(d)^(T*) ×F(d,Vrad)×MDT(d)^(T)|  (eq. 11)in which equation the operators T and * designate the transpositiontransconjugation operations of a matrix.

Applying these filters simultaneously may eliminate reflectors resultingfrom the clutter, reinforces any concealed targets, and performs thevelocity processing known by those skilled in the art of radars. Thisvelocity processing makes it possible to form a distance-radial velocitycartography of the processing zone ZT.

The value MDV(d,Vrad) is an estimate, in the sense of processing of thesignal, of the energy remaining after elimination of the clutter, in thedistance velocity d, Vrad cell. As a result: if a target is present inthat cell, MDV(d,Vrad) measures the energy of that target; otherwise,MDV(d,Vrad) is a noise measurement in that cell.

FIG. 14 illustrates the effect of this “long time” filtering for adistance d relative to the FTT velocity processing over a “short time”illustrated in FIG. 13 as used in the state of the art. In these twofigures, the noise is shown by two zones 132 and 142. The clutter 131appearing in FIG. 13 is eliminated in FIG. 14, and a concealed target143 then appears, surrounded by noise 142.

According to an exemplary embodiment, the radial velocity resolutionused in the invention (FIG. 14) is much smaller than for the traditional“short time” velocity processing (m·Tr, FIG. 13), due to the timedifference.

Step E42 is a step for estimating the noise for each distance-radialvelocity cell of the processing zone ZT.

In some embodiments, this noise level is estimated by an obliqueprojection method identical to that used to create the filters in stepP5:NB(d,Vrad)=MDT^(T*)(d)·Porth(d)·MDT(d)^(T)−MDV(d,Vrad)  (eq. 12)

This estimate of the noise level for a given distance radial velocityonly uses the distance profiles MDT(d) collected at that distance.

During a step E43, the device 10, according to an exemplary embodiment,computes the signal-to-noise energy ratio RSB on the distance-radialvelocity d, Vrad cell.

$\begin{matrix}{{{RSB}\left( {d,{Vrad}} \right)} = \frac{{MDV}\left( {d,{Vrad}} \right)}{{NB}\left( {d,{Vrad}} \right)}} & \left( {{eq}.\mspace{11mu} 13} \right)\end{matrix}$

During the same step E43, the device 10 may perform the detection in thesense of processing of the signal by comparing said ratio RSB to athreshold, a target being detected when the ratio RSB exceeds thatthreshold. The detection may be performed in a different step in otherembodiments.

The detection threshold may be set from the probability of false alarmsdesired by the system and the number of strong reflectors to beeliminated per distance cell. This detector may be called “zero-forcingmatched subspace detector.” It is adapted to the use of obliqueprojection filters as used in these embodiments.

In other embodiments, the steps E42 for estimating the noise level andstep E43 for detection are done according to the state of the art usinga CFAR detector. In particular, this detector may be applied when thefilter created in P5 is an orthogonal projection, followed by acorrelation.

The disclosure is described above with reference to drawings. Thesedrawings illustrate certain details of specific embodiments thatimplement the systems and methods and programs of the presentdisclosure. However, describing the disclosure with drawings should notbe construed as imposing on the disclosure any limitations that may bepresent in the drawings. The present disclosure contemplates methods,systems and program products on any machine-readable media foraccomplishing its operations. The embodiments of the present disclosuremay be implemented using an existing computer processor, or by a specialpurpose computer processor incorporated for this or another purpose orby a hardwired system. No claim element herein is to be construed underthe provisions of 35 U.S.C. §112, sixth paragraph, unless the element isexpressly recited using the phrase “means for.” Furthermore, no element,component or method step in the present disclosure is intended to bededicated to the public, regardless of whether the element, component ormethod step is explicitly recited in the claims.

As noted above, embodiments within the scope of the present disclosureinclude program products comprising machine-readable media for carryingor having machine-executable instructions or data structures storedthereon. Such machine-readable media can be any available media whichcan be accessed by a general purpose or special purpose computer orother machine with a processor. By way of example, such machine-readablemedia can comprise RAM, ROM, EPROM, EEPROM, CD ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium which can be used to carry or store desired program code inthe form of machine-executable instructions or data structures and whichcan be accessed by a general purpose or special purpose computer orother machine with a processor. Machine-readable media may benon-transitory. When information is transferred or provided over anetwork or another communications connection (either hardwired,wireless, or a combination of hardwired or wireless) to a machine, themachine properly views the connection as a machine-readable medium.Thus, any such a connection is properly termed a machine-readablemedium. Combinations of the above are also included within the scope ofmachine-readable media. Machine-executable instructions comprise, forexample, instructions and data which cause a general purpose computer,special purpose computer, or special purpose processing machines toperform a certain function or group of functions.

Embodiments of the disclosure are described in the general context ofmethod steps which may be implemented in one embodiment by a programproduct including machine-executable instructions, such as program code,for example, in the form of program modules executed by machines innetworked environments. Generally, program modules include routines,programs, objects, components, data structures, etc., that performparticular tasks or implement particular abstract data types.Machine-executable instructions, associated data structures, and programmodules represent examples of program code for executing steps of themethods disclosed herein. The particular sequence of such executableinstructions or associated data structures represent examples ofcorresponding acts for implementing the functions described in suchsteps.

Embodiments of the present disclosure may be practiced in a networkedenvironment using logical connections to one or more remote computershaving processors. Logical connections may include a local area network(LAN) and a wide area network (WAN) that are presented here by way ofexample and not limitation. Such networking environments are commonplacein office-wide or enterprise-wide computer networks, intranets and theInternet and may use a wide variety of different communicationprotocols. Those skilled in the art will appreciate that such networkcomputing environments will typically encompass many types of computersystem configurations, including personal computers, hand-held devices,multi-processor systems, microprocessor-based or programmable consumerelectronics, network PCs, servers, minicomputers, mainframe computers,and the like. Embodiments of the disclosure may also be practiced indistributed computing environments where tasks are performed by localand remote processing devices that are linked (either by hardwiredlinks, wireless links, or by a combination of hardwired or wirelesslinks) through a communications network. In a distributed computingenvironment, program modules may be located in both local and remotememory storage devices.

An exemplary system for implementing the overall system or portions ofthe disclosure might include a general purpose computing device in theform of a computer, including a processing unit, a system memory, and asystem bus that couples various system components including the systemmemory to the processing unit. The system memory may include read onlymemory (ROM) and random access memory (RAM). The computer may alsoinclude a magnetic hard disk drive for reading from and writing to amagnetic hard disk, a magnetic disk drive for reading from or writing toa removable magnetic disk, and an optical disk drive for reading from orwriting to a removable optical disk such as a CD ROM or other opticalmedia. The drives and their associated machine-readable media providenonvolatile storage of machine-executable instructions, data structures,program modules, and other data for the computer.

It should be noted that although the flowcharts provided herein show aspecific order of method steps, it is understood that the order of thesesteps may differ from what is depicted. Also two or more steps may beperformed concurrently or with partial concurrence. Such variation willdepend on the software and hardware systems chosen and on designerchoice. It is understood that all such variations are within the scopeof the disclosure. Likewise, software and web implementations of thepresent disclosure could be accomplished with standard programmingtechniques with rule based logic and other logic to accomplish thevarious database searching steps, correlation steps, comparison stepsand decision steps. It should also be noted that the word “component” asused herein and in the claims is intended to encompass implementationsusing one or more lines of software code, and/or hardwareimplementations, and/or equipment for receiving manual inputs.

The foregoing description of embodiments of the disclosure have beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the disclosure to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of the disclosure. Theembodiments were chosen and described in order to explain the principalsof the disclosure and its practical application to enable one skilled inthe art to utilize the disclosure in various embodiments and withvarious modifications as are suited to the particular use contemplated.

What is claimed is:
 1. A method implemented in a mobile systemcomprising a radar for detecting, in a scene, at least one targetreflector of a first predetermined type, called target type, that may beconcealed by at least one high-energy reflector of a second type, calledstrong type, said method comprising: a step for identifying a zone of adistance-radial velocity space that includes high-energy reflectorsconfigured to conceal the target reflectors; a step for modeling anorder two phase shift over time, due to the Doppler effect, oftheoretical reflectors of said target type and theoretical reflectors ofsaid strong type, the modeling using a kinematic signature of saidtheoretical reflectors; a step for creating a filter for at least onedistance and one radial velocity given by: a phase shift of atheoretical target reflector at the at least one distance and for theone radial velocity; and a phase shift of a theoretical strong reflectorat the at least one distance and for each radial velocities of the zone;said phase shifts being obtained from the aforementioned step formodeling, said filter being designed to attenuate, by projection, theenergy of the high-energy reflectors of said scene and increase, bycorrelation, the energy of said at least one target reflector of thescene at the given distance and for the given radial velocity; a stepfor illuminating the scene, by controlling the radar, and acquiring rawradar data from echoes reflected by the reflectors of the scene; a stepfor obtaining distance profiles obtained by processing raw radar data toseparate the reflectors of the scene in terms of distance, said profilesbeing collected over a long enough time for the distance variation of areflector of the scene to be able to be considered quadratic relative tothe time; a step for applying filters on said distance profiles, thisstep leading to a separation of the reflectors of the scene in velocity;and a step for detecting the target reflectors among the high-energyreflectors.
 2. The method according to claim 1, wherein said filter isan oblique projector.
 3. The method according to claim 1, wherein saididentification step comprises: a step for building a distance-radialvelocity cartograph resulting from the raw radar data observed during ashort time; and a step for analyzing the distance-radial velocitycartograph.
 4. The method according to claim 1, wherein the step foridentifying the zone in the distance-radial velocity space is performedfrom a priori knowledge of the observation geometry, of the antennadiagram of said radar and of the characteristics of the flight of thesystem.
 5. The method according to claim 1, wherein said step forobtaining the distance profiles comprises a processing for compensatingthe distance migration of the reflectors over a long time.
 6. The methodaccording to claim 1, wherein the detection step uses a detector of theCFAR type.
 7. The method according to claim 1, wherein the step fordetecting the target reflectors and estimating the noise level, for adistance-radial velocity cell, uses only said collector distanceprofiles, at that distance.
 8. The method according to claim 1, whereinsaid step for illuminating the scene uses a waveform of the FMCW type.9. The method according to claim 1, wherein said kinematic signature ofsaid target reflectors is defined by a zero orthoradial velocity. 10.The detection method according to claim 1, wherein said steps foridentifying zones and for creating filters are performed before, after,or in parallel with steps for acquiring raw radar data and for obtainingdistance profiles.
 11. A tangible non-transitory computer-readablestorage medium having machine instructions stored thereon, theinstructions being executable by a processing circuit to cause theprocessing circuit to perform operations comprising: identifying a zoneof a distance-radial velocity space that includes a plurality ofhigh-energy reflectors, wherein at least one high-energy reflectorconceals at least one target reflector; modeling an order two phaseshift over time, due to the Doppler effect, of theoretical reflectors ofsaid target type and theoretical reflectors of said strong type, themodeling using a kinematic signature of said theoretical reflectors;creating a filter for at least one distance and one radial velocitybased on: a phase shift of a theoretical target reflector at the atleast one distance and for the one radial velocity; and a phase shift ofa theoretical strong reflector at the at least one distance and for eachradial velocities of the zone; wherein the phase shifts are obtainedfrom the modeling, wherein the filter attenuates, by projection, theenergy of the high-energy reflectors of said scene and increases, bycorrelation, the energy of said at least one target reflector of thescene at the given distance and for the given radial velocity;illuminating the scene, by controlling the radar, and acquiring rawradar data from echoes reflected by the reflectors of the scene;obtaining distance profiles obtained by processing raw radar data toseparate the reflectors of the scene in terms of distance, said profilesbeing collected over a long enough time for the distance variation of areflector of the scene to be able to be considered quadratic relative tothe time; applying filters on said distance profiles, this step leadingto a separation of the reflectors of the scene in velocity; anddetecting, in the scene, at least one target reflector from among theplurality of high-energy reflectors.
 12. A device incorporated in amobile system to detect, in a scene, at least one target reflector of afirst predetermined type, called target type, that may be concealed byat least one high-energy reflector of a second type, called strong type,said mobile system comprising: a radar configured to illuminate thescene and acquire raw radar data from echoes reflected by the reflectorsof the scene; means for identifying a zone of a distance-radial velocityspace that includes high-energy reflectors configured to conceal thetarget reflectors; means for modeling an order two phase shift overtime, due to the Doppler effect, of theoretical target reflectors andtheoretical strong reflectors, the modeling using a kinematic signatureof at least one theoretical reflector; means for creating a filter forat least one distance and one radial velocity given by: the phase shiftof a theoretical target reflector at the at least one distance and forthe one radial velocity; and the phase shift of a theoretical strongreflector at the at least one distance and for each radial velocities ofthe zone; said phase shifts being obtained from the modeling, saidfilter being designed to attenuate, by projection, the energy of thehigh-energy reflectors of said scene and increase, by correlation, theenergy of said at least one target reflector of the scene at the givendistance and for the given radial velocity; means for obtaining distanceprofiles obtained by processing raw radar data to separate thereflectors of the scene in terms of distance, said profiles beingcollected over a long enough time for the distance variation of areflector of the scene to be able to be considered quadratic relative tothe time; means for applying filters on said distance profiles, thisstep leading to a separation of the reflectors of the scene in velocity;and means for detecting the target reflectors among the high-energyreflectors.